Methods of making aluminum lead alloys

ABSTRACT

The invention concerns aluminium-lead ingots or other articles as well as bearings and other products made therefrom and also to methods of making such ingots or other articles. The improved aluminium-lead ingot is made from an aluminium-tin ingot having a substantially continuous tin rich network which is expelled from the aluminium matrix and replaced by lead in the network passages originally occupied by the tin rich phase.

United States Patent 11 1 v 1111 3,8373% Stern Sept. 24, 1974 METHODS OF MAKING ALUMINUM LEAD ALLOYS Primary ExaminerLc0n D. Rosdol Assistant Examiner-Edith Rollins {76] lnvemor' E i Studley Park gtitsrgglzley, Agent, or Firm--Waters, Roditi, Schwartz &

[22] Filed: Dec. 15, 1972 [21] Appl. No.: 315,670

[57] ABSTRACT [30] Foreign Application Priority Data The invention concerns aluminium-lead ingots or Dec. 17, 1971 Australia 7438/71 other articles as as bearings and other Products made therefrom and also to methods of making such 52 us. (:1 117/114 R, 75/138, 117/51 ingots or other articles. The improved aluminium-lead [51] int. Cl. C23c 1/06 ingot is made from an aluminium'tin h1g0t having a [58] Fi ld f S h 117/114 R, 50, 1 52; substantially continuous tin rich network which is ex- 75/133 pelled from the aluminium matrix and replaced by lead in the network passages originally occupied by [56] References Cited the tin rich P FOREIGN PATENTS OR APPLICATIONS 3 Claims, 3 Drawing Figures 295,322 2/1966 Australia PATENTEB SEP24I974 METHODS OF MAKING ALUMINUM LEAD ALLOYS This invention relates to aluminium-lead ingots or other articles as well as bearings and other products made therefrom and also to methods of making such ingots or other articles. The new ingot is particularly adapted for use in the manufacture of bearings for internal combustion engines but the invention is not limited thereto as the improved product may obviously be used for a wide variety of other purposes.

The casting of aluminium-tin ingots and their conversion to strip for bearings is described for example, in the specification of the Repco Australian Pat. No. 249218. The use of lead in lieu of tin in such an alloy is also described for example, in the specification of the Repco Australian Pat. No. 295322.

It is well-known that lead is normally much cheaper than tin and furthermore that aluminium-lead bearings have properties as good as or better than aluminium-tin bearings. However, it has not previously been considered possible to produce a satisfactory aluminium-lead ingot for such a purpose having a relatively high lead content. Hitherto, the lead content in aluminium-lead ingots was normally in the region of 8 percent by weight and was not present in the form of a continuous network but in the form of spheroids.

Lead has no solid solubility in aluminium and very low liquid solubility. For example, at l,OOOC. aluminium will dissolve not more than about 12 percent by weight of lead whilst at 850C. a lead content of 7 percent by weight only is attainable. Even if an aluminiumlead ingot is cast at the relatively high temperatures mentioned the aforesaid relatively low lead content still tends to segregate before the aluminium has solidified, the lead remaining in suspension in the form of spheroids.

The primary object of the present invention is to provide an improved aluminium-lead ingot or other article containing a materially increased percentage of lead which is distributed throughout the aluminium matrix in the form of a substantially continuous network.

Another object is to provide improved methods of making an aluminium-lead ingot or other article having a relatively high lead content as aforesaid.

A further object is to provide improved apparatus for carrying out the methods of making the improved aluminium-lead ingot or other article.

According to the present invention the improved aluminium-lead ingot or other article has a lead content which is distributed throughout the aluminium matrix in the form of a substantially continuous network.

The improved aluminium-lead ingot or other article is made from aluminium-tin ingot or other article having a sufficient tin content to ensure that the tin is present in the form of a substantially continuous network by a method which includes the steps of placing at least one surface of the aluminium-tin article into contact with a pool of molten lead, heating said aluminium-tin article until a temperature is reached which is at least that of the melting point of lead but below that of aluminium so as to melt the tin network and cause the molten tin to dissolve a percentage of aluminium defined by the maximum temperature reached, causing said tin rich liquid to be expelled from its substantially continuous network passages in the aluminium matrix and to be replaced in said passages by lead from the pool.

A further feature of the invention concerns apparatus for carrying out the improved method, the apparatus including a receptacle having an apertured bottom merging into a continuous side wall and means for effecting'a detachable sealing connection between the apertured bottom portion of said receptacle and a free surface on said aluminium-tin article, said receptacle being adapted either to receive tin rich liquid expelled from the last mentioned article or alternatively to hold a predetermined quantity of lead which is intended to replace the tin rich phase in said article.

The above and other objects and features of the invention will however be more readily apparent from the following detailed description of several practical embodiments of the invention.

Referring to the drawings:

FIG. 1 is a diagrammatic sectional elevation showing an open topped receptacle secured to the upper surface of an aluminium-tin ingot which has been immersed in a pool of molten lead.

FIG. 2 shows another arrangement involving the use of two receptacles. In this case an upper receptacle contains a predetermined quantity of molten lead and the aluminium-tin ingot and a lower receptacle are immersed in a pool of molten neutral salt.

FIG. 3 is a further embodiment also involving the use of two receptacles, the upper receptacle being provided with means for accelerating the process and for indicating when it has been completed.

In accordance with the embodiment seen in FIG. 1 of the drawings an open topped receptacle 2 is detachably connected by any suitable means such as clamps or ties 3 to the upper surface of an aluminium-tin ingot or other article 4 having a tin content of at least 7 percent by weight and which is distributed substantially evenly throughout the aluminium matrix in the form of a substantially continuous network.

The receptacle in this case is open at the top and bottom and has an upstanding endless side wall 6 having a lower edge of knife-edged formation 7 so that it may penetrate the supper surface of the ingot and thus form a sealing connection therewith.

The aluminium-tin ingot 4 and the receptacle 2 carried thereby are immersed in a pool of molten lead 8 so that the upper surface 9 of the ingot is substantially parallel with but below the level 11 of the lead pool.

The temperature of the lead pool should not approach the melting point of aluminium, namely 660 C. the melting point of lead being 327 C. A maximum temperature of 560 C. is satisfactory although slightly higher temperatures may be used with care. It has been ascertained that as the temperature of the aluminiumtin ingot rises, the tin network in the ingot is caused to melt and dissolve a percentage of aluminium defined by the maximum temperature reached. This tin rich liquid is expelled from its network passages in the aluminium matrix by molten lead from the pool. The inflowing lead thus fills the network originally occupied by the tin rich liquid.

It will be appreciated that the time required for such a replacement of the original tin content by the lead is dependent upon the temperature employed and the depth of the ingot in the pool of lead. Obviously the greater the height of the side wall 6 of the receptacle in the lead pool as seen in FIG. 1, the greater the head of the lead pool above the ingot and consequently the height of this head materially affects the rate at which the exchange between the tin rich phase of the ingot and the lead will take place.

When the lead exchange has been completed, the ingot and its receptacle 2 are removed from the lead pool 8 and the liquid in the receptacle above the ingot 4 poured off prior to the receptacle being removed from the ingot and the latter allowed to cool. If such an ingot is required for making bearings for internal combustion engines for example, the ingot is preferably reduced by rolling or in any other suitable manner to the required thickness before being bonded to a steel backing strip and cut and shaped to predetermined size.

According to a modification as seen in FIG. 2, the replacement of the tin content by lead in the aluminium matrix takes place in the opposite direction. in this case two oppositely disposed receptacles 2 and 14 are employed, one of the receptacles 2 being sealingly connected to the upper surface of the ingot whilst the other receptacle 14 is provided with a bottom closure and sealingly connected to the lower surface of the ingot. The two receptacles may be connected together by tie rods 3. The lower receptacle is either vented in any suitable manner or connected to a source of vacuum so that the pressure therein may be reduced below atmospheric pressure if so desired.

' A predetermined quantity of molten lead 12 is poured into the receptacle 2 so as to form a pool of lead upon the upper surface of the ingot 4 which in this case is immersed or partly immersed in a pool 13 of molten neutral salt.

As the tin content in the ingot melts it dissolves a percentage of aluminium defined by the maximum temperature reached and thus forms a tin rich liquid. The latter is expelled from its network passages in the aluminium matrix under the hydrostatic pressure of the lead pool 12 which refills the network originally occupied by the tin richliquid.

Once again the time required for completing the exchange of tin by the lead in the ingot is dependent upon the temperature employed and the pressure differential between the pool of molten lead above the upper surface of the ingot and the pressure in the lower receptacle 14. This exchange of the tin rich liquid by lead is of course accelerated if the pressure in the lower receptacle 14 is reduced below atmospheric pressure.

A still further embodiment is diagrammatically illustrated in FIG. 3 which employs other apparatus designed to speed up the process of exchanging the tin by lead in the aluminium matrix of the ingot.

In this case the receptacle 2 mounted upon the upper surface of the ingot is provided with a top wall 16 having an exhaust port 17 so that it may be detachably connected to a pump or other suitable source of vacuum 18. By this arrangement, the pressure above the ingot 4 may be rapidly reduced below that of atmospheric pressure. If desired, the ingot 4 may also be fitted with a second receptacle 18 connected to the bottom of the ingot so as still further to improve the heat transfer from the pool of molten lead in which the ingot and the lower receptacle are immersed.

if desired, means may be provided for giving the operator an audible or visual warning when a predetermined quantity of lead has been exchanged for the aforesaid tin rich liquid. For this purpose a manually adjustable probe 21 may be provided which is electrically connected to an electric lamp 22 or audible alarm through a battery 23 and a return lead 24 for example to the upper receptacle 2 which in this case is composed of metal.

The probe may be mounted in a substantially upright bushing 26 electrically insulated from the receptacle so that the lower end of the probe which may be pointed may be moved towards and away from the upper surface of the ingot.

It will be appreciated from the foregoing that as the upper housing employed in FIG. 3 is provided with a top cover, undesirable oxidation of the ingot and the tin being expelled therefrom is either prevented or reduced to a minimum and subsequent recovery of the tin and other metal is facilitated.

Additional well-known alloying elements such as copper and silicon may if desired be included in the original aluminium-tin ingot or other article. Any of these additional alloying elements that may be employed and which will also dissolve in the original tin network, may facilitate the desired replacement by the lead.

A small percentage of tin for example 5 percent of the lead may be added thereto to improve its corrosion resistance and this is particularly desirable if the aluminium lead ingot is to be subsequently made into bearings.

According to a practical embodiment a cast ingot of aluminium-tin is employed. This ingot may comprise 10 percent tin and 1 percent copper by weight and the remainder aluminium. The two major surfaces such as the upper and lower surfaces of the ingot are preferably machined substantially flat and parallel if not in that condition when cast.

The aforesaid receptacles are preferably made of stainless steel and if an open topped receptacle is em ployed as in FIG. 1 a thin layer of molten lead or other suitable material is preferably initially poured onto the upper surface of the ingot in order to prevent oxidation of this surface during the exchange process of the tin by the lead.

it has been ascertained that if an aluminium tin ingot of approximately 3 centimeters thick is employed with a lead pool temperature of 550 C. to 560 C. together with a vacuum in the upper receptacle 2 of approximately centimeters of mercury, a layer of lead of approximately 8 millimeters will form on the top of the ingot in about 10 minutes after the continuous network therein has been filled with lead as aforesaid.

After this exchange has been completed, the ingot may if desired be raised slightly so that its lower surface is just clear of the surface of the lead in the pool. By

continuing to maintain the aforesaid suction in the upper receptacle, the molten lead in the network in the aluminium matrix will continue to move upwardly so as to leave a predetermined part of the bottom portion of the ingot free of lead. This materially improves subsequent bonding with a steel strip or other support in accordance with known workshop practice.

As seen in FIG. 3 of the drawings the lower receptacle 14 is open at the bottom and if desired provided with a plurality of slots or other apertures 26 to facilitate contact of the ingot with the molten lead in the pool, and avoid the possibly trapping of gases in the lower receptacle. The lower receptacle in this case serves to continue to conduct heat from the pool to the ingot after the latter has been raised clear of the surface of the molten lean in the pool as above-mentioned. The insulated probe 21 may be employed to indicate the height of the molten metal above the ingot in the upper receptacle thereby indicating how much of the network in the bottom portion of the ingot which has been freed of lead under the influence of the source of vacuum 18.

The improved aluminium-lead product has proved to be particularly advantageous in view of its relatively high lead content which is distributed substantially evenly throughout the aluminium matrix. Aluminiumlead bearings in accordance with the present invention have proved to be most satisfactory. In this regard it will be obvious that the invention is necessarily not restricted to use in such bearings but that the desirable properties of the improved aluminum-lead product aluminium-lead render it suitable for a wide variety of other uses.

It will also be understood that various alterations, modifications and/or additions may be introduced into the foregoing without departing from the ambit of the invention as defined by the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A method of making an aluminium-lead article from an aluminium-tin article having a sufficient tin content to ensure that the tin is present in the form of a substantially continuous network, said method comprising the steps of placing at least one surface of the aluminium-tin article into contact with a pool of molten lead, heating said aluminium-tin article until a temperature is reached which is at least that of the melting point of lead but below that of aluminium so as to melt the tin network and cause the molten tin to dissolve a percentage of aluminium defined by the maximum temperature reached, causing said tin rich liquid to be expelled from its substantially continuous network passages in the aluminium matrix and to be replaced in said passages by lead from the pool.

2. A method according to claim 1 wherein the expulsion of the tin from said substantially continuous network passages is effected by creating a pressure differential between said surface of the article in contact with the lead pool and at least one other surface of the aluminium-tin article.

3. Improvements relating to the making of an aluminium-lead article from an aluminium-tin article in which the minimum tin content is at least 7 percent by weight to ensure the tin being present in the form of a substantially continuous network characterized by the steps of securing a receptacle to the upper surface of said aluminium tin article, said receptacle having an apertured bottom and an endless side wall adapted to form a sealing connection with said article, immersing said aluminium-tin article and part of said receptacle in a pool of molten lead which serves to heat said article until a temperature is reached which is not less than the melting point of lead but below that of aluminium whereupon said tin network is caused to melt and to dissolve a percentage of aluminium defined by the maximum temperature reached thus forming a tin rich liquid which flows upwardly into said receptacle by the hydrostatic pressure of the lead in the pool leaving in the aluminium the network passages originally occupied by the tin rich liquid and now filled by lead from the pool. 

2. A method according to claim 1 wherein the expulsion of the tin from said substantially continuous network passages is effected by creating a pressure differential between said surface of the article in contact with the lead pool and at least one other surface of the aluminium-tin article.
 3. Improvements relating to the making of an aluminium-lead article from an aluminium-tin article in which the minimum tin content is at least 7 percent by weight to ensure the tin being present in the form of a substantially continuous network characterized by the steps of securing a receptacle to the upper surface of said aluminium tin article, said receptacle having an apertured bottom and an endless side wall adapted to form a sealing connection with said article, immersing said aluminium-tin article and part of said receptacle in a pool of molten lead which serves to heat said article until a temperature is reached which is not less than the melting point of lead but below that of aluminium whereupon said tin network is caused to melt and to dissolve a percentage of aluminium defined by the maximum temperature reached thus forming a tin rich liquid which flows upwardly into said receptacle by the hydrostatic pressure of the lead in the pool leaving in the aluminium the network passages originally occupied by the tin rich liquid and now filled by lead from the pool. 